Caption: Pollen corona. Church steeple in front of a corona (luminous disk) around the Moon. A corona is an optical atmospheric effect, which in this case has been caused by a high concentration of pine tree pollen in the atmosphere. Coronas consist of one or more rings, some of which may be coloured, around the Sun or Moon. They are caused by the diffraction of light by particles in the air, most commonly small water droplets in clouds. This corona's elliptical shape is thought to be due to the pollen's non-spherical shape. Photographed in Finland.